<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .box{
            border: 5px solid yellow;
            margin: 50px auto;
            display: none;
            flex-wrap: wrap;
        }
        .item{
            width: 50px;
            height: 50px;
            box-sizing: border-box;
            border: 1px solid #ccc;
            background: #555;
            color: purple;
            text-align: center;
            font-weight: bold;
            line-height: 50px;
            font-size: 20px;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="item" data-index="1"></div>
        <div class="item" data-index="2"></div>
        <div class="item" data-index="3"></div>
        <div class="item" data-index="4"></div>
        <div class="item" data-index="7"></div>
        <div class="item" data-index="8"></div>
        <div class="item" data-index="9"></div>
        <div class="item" data-index="10"></div>
        <div class="item" data-index="13"></div>
        <div class="item" data-index="14"></div>
        <div class="item" data-index="15"></div>
        <div class="item" data-index="16"></div>
        <div class="item" data-index="18"></div>
        <div class="item" data-index="19"></div>
        <div class="item" data-index="20"></div>
        <div class="item" data-index="21"></div>
    </div>
    <script src="./saolei.js"></script>
</body>
</html>